Time for arithmetic! DI Sweet Sixteen breakdown by conference, BCS and otherwise:

ACC: two teams (no teams seeded lower than fourth)
Big East: two teams (no teams seeded lower than fourth)
Big Ten: no teams in the Sweet Sixteen! (When was the last time this happened?) (See update, above.)
Big Twelve: four teams (no team seeded lower than fourth)

Pac-10: one team (no teams seeded lower than fourth)
SEC: four teams (two teams seeded lower than fourth)
So-called mid-majors, including the MWC: three teams (two teams seeded lower than fourth): Xavier (#3, A-Ten), Gonzaga (#7, WCC), San Diego State (#11, Mountain West)

Conference records so far (assuming my math is correct):

ACC: 4-4
America East: 1-2
A-Ten: 4-2
Big East: 7-4

Big Ten: 3-4
Big XII: 10-3
Horizon: 1-2
MWC: 2-1

Pac-10: 3-1
SEC: 10-2